<template>
  <ul class='list'>
    <li class='item' 
    v-for='(item,key) of letters' 
    :key='item' 
    :ref='item'
    @click="handleLetterClick"
    @touchstart='handleTouchStart'
    @touchmove='handleTouchmove'
    @touchend='handleTouchEnd'
    >
      {{item}}
    </li>
  </ul>
</template>

<script>
export default {
  name: 'CityAiphader',
  props:{
    cities:Object
  },
  data() { 
    return {
      touchStatus:false,
      startY:0
    }
  },
  updated(){
    this.startY=this.$refs['A'][0].offsetTop
  },
  methods: {
    handleLetterClick(e){
      this.$emit('change',e.target.innerText)

    },
    handleTouchStart(){
      this.touchStatus=true
      
    },
    handleTouchmove(e){
      if(this.touchStatus){
        //函数节流
        if(this.timer){ 
          clearTimeout(this.timer)
        }
        this.timer=setTimeout(() => {
          const touchY=e.touches[0].clientY-122
          console.log(touchY);
          const index=Math.floor((touchY-this.startY)/23)
          console.log(index);
          if(index>=0&&index<this.letters.length){
            this.$emit('change',this.letters[index])
          }
        }, 16);
      }
    },
    handleTouchEnd(){
      this.touchStatus=false
    }
  },
  mounted() {

  },
  computed: {
    letters(){
      const letters=[]
      for(let i in this.cities){
        letters.push(i)
      }
      return letters
    }
  },
 }
</script>

<style lang="stylus" scoped>
@import '~styles/varibles.styl';
.list
  display:flex
  flex-direction:column
  justify-content:center
  position:absolute
  top:1.58rem;
  right:0;
  bottom:0
  width:0.44rem;
  // background:red
  .item
    line-height:0.3rem;
    text-align:center;
    color:$bgColor
</style>